Vary colors of axis labels in R based on another variable

Question

I usually use ggplot2, but in this case I am using the regular image() function to plot a heatmap of a large data set. I can label all the labels as re

Answer 1

I like very much thelatemail's approach, and can only add a small refinement since the fixed "at" positions (as in the example above with at = 1:3) didn't work well for me. In my case, I needed to generate a barplot and provided my own values for space and width parameters. In the end what I used looks like (example with random data in which I wanted the bars and labels for positive (non-negative, to be more precise) data values to be green and red otherwise. For this example I also use the letters function to provide labels and rotate the labels using las = 2):

x <- rnorm(26)
color <- rep("green", length(x))
color[x < 0] <- "red"

par(mar=c(6,4.1,4.1,2.1))
barplot(x, las = 2, ylim = c(min(x)-0.5, max(x)+0.5), col = color, space = 0.5, width = 2)    
Map(function(x,y,z) 
axis(1,at=x,col.axis=y,labels=z,lwd=0,las=2),
seq(from = 2, by = 3, length.out = length(x)),
color,
letters
)
axis(1,at=seq(from = 2, by = 3, length.out = length(x)),labels=FALSE)